In Japanese Patent Laid-Open No. 2014-170123, a lens unit is disclosed which is provided with a structure for restraining distortion of a glass lens which is held on a lens frame by press fitting. In the lens unit described in this Patent Literature, an excessive pressure is restrained from being applied to the glass lens, the lens frame and a holder at the time of press fitting and thereby distortion of the glass lens held by the lens frame due to press fitting is suppressed.
In Japanese Patent Laid-Open No. 2015-175918, a wide angle lens unit is disclosed which is provided with a structure for aligning by utilizing a glass lens which is held by a lens holder. In the wide angle lens unit described in this Patent Literature, a position of a first holder is adjusted by an aligning pin inserted through an opening part for alignment and then the first holder is fixed to a second holder and, in this manner, alignment is performed by utilizing a glass lens held by the lens holder.
With requirements for optical performance of the entire lens unit become strict, molding accuracy for each of lenses has been required to improve. A plastic lens is capable of suppressing cost lower than a glass lens, but a variation of its refractive index with respect to a temperature change is large. Therefore, in order to improve temperature characteristics of the lens unit, it is preferable to utilize a glass lens. However, especially, although a glass lens produced by being polished with a grindstone or the like is capable of suppressing a surface accuracy error of its lens face but the glass lens is difficult to attain a high degree of molding accuracy. For example, an error of about several tens of μm is occurred in molding accuracy in lens thickness of a glass lens in comparison with molding accuracy in thickness of a plastic lens which is suppressed to an error of about several μm. Therefore, it is difficult to attain required optical performances, especially, to suppress a cause of focus deviation.
In the former Patent Literature (Japanese Patent Laid-Open No. 2014-170123), a structure is disclosed that, in a case that a glass lens is press-fitted to an inner side of a lens frame and the lens frame is press-fitted to an inner side of a holder, an excessive pressure is restrained from being applied to the glass lens, the lens frame and the holder at the time of press-fitting and, when temperature change is occurred, concentration of stress to specific portions of the glass lens, the lens frame and the holder is relaxed. In this case, in the lens holding part to which the glass lens is press-fitted, a tip end face (face on the object side), which is perpendicular to an optical axis, of an object side glass lens insertion part of the lens holding part is abutted with an adjacent lens on the object side. Further, in the lens holding part to which the glass lens is press-fitted, a protruded part extended in a circumferential direction on an outer peripheral side of an end face of an image side glass lens insertion part of the lens holding part is abutted with an adjacent lens on the image side. Alternatively, a plurality of protruded parts (faces on the image side) separated from each other in the circumferential direction are abutted with an adjacent lens on the image side. However, the structure in the former Patent Literature is provided with no adjusting structure for adjusting a space in the optical axis direction between the glass lens and a lens adjacent to the glass lens. Therefore, the space in the optical axis direction between the glass lens and the adjacent lens cannot be adjusted.
In the latter Patent Literature (Japanese Patent Laid-Open No. 2015-175918), a structure is disclosed that a position of a first holder by which a glass lens is held is adjusted by a centering pin inserted into a centering opening part formed in a second holder which holds the first holder on its inner side. Centering is performed so that the position of the glass lens is adjusted in a direction perpendicular to the optical axis. However, the structure in the latter Patent Literature is provided with no adjusting structure for adjusting a space in the optical axis direction between the glass lens and a lens adjacent to the glass lens. Therefore, the space in the optical axis direction between the glass lens and the adjacent lens cannot be adjusted.
Accordingly, in a lens unit into which the glass lens is assembled, a structure is required which is capable of restraining trouble such as focus deviation caused by a molding error of the glass lens.